Kraken

The Kraken is an old a terrible monster that swims in the deepest recesses of the ocean. No one has ever seen its face, in fact most who see it don't live to tell the tale. It attacks ships with it's large tentacles. The tentacles are big enough to wrap around cargo ships and crush them. It's very presence churns the water and turns the ocean to chaos.
Any wise sailor knows to keep a vigilant eye when on the waters. If you rest for to long the Kraken is sure to take you.